Particulate filter

Abstract

An object of the invention is to suppress deposition of ash in a wall-flow particulate filter while curtailing drops in a trapping rate of PM. To attain the above object, the invention provides a wall-flow particulate filter delimited by porous partition walls having pores of a size that allows ash and ash aggregates to pass therethrough. In the filter, a coat layer having pores smaller than the pores of the partition walls is provided, at a region of the partition walls, from an upstream end thereof up to a position before a downstream end thereof.

The invention claimed is: 
     
       1. A particulate filter, comprising:
 a plurality of first passages, the ends of the first passages being blocked on an upstream-side in a flow direction of exhaust gas; 
 a plurality of second passages, the ends of the second passages being blocked on a downstream side in the flow direction of exhaust gas; 
 porous partition walls that are members that separate the first passages from the second passages, the porous partition walls having pores of a size such that ash passes through the pores; and 
 a porous coat layer provided at part of a region of the partition walls from an upstream end of the partition walls up to a position before a downstream end of the partition walls, the porous coat layer having pores smaller than the pores of the partition walls, and a thickness of the porous coat layer decreasing gradually from the end of the upstream side of the porous coat layer towards the downstream side of the porous coat layer. 
 
     
     
       2. The particulate filter according to  claim 1 , wherein
 a catalyst having oxidizing ability is supported at a region of the partition walls at which the porous coat layer is not provided. 
 
     
     
       3. The particulate filter according to  claim 1 , wherein
 the pores of the porous partition walls have an average pore size that ranges from 25 μm to 50 μm. 
 
     
     
       4. The particulate filter according to  claim 1 , wherein
 the porous coat layer is a dispersion, the dispersion being made up of particles having an average particle size ranging from 1 μm to 10 μm. 
 
     
     
       5. The particulate filter according to  claim 1 , wherein
 the porous coat layer comprises a metal, the ionization tendency of which is greater than that of a main component of the ash.